The heart is the muscle in the body responsible for pumping and circulating blood throughout the body. The heart achieves this circulatory action by rhythmically contracting its inner and outer walls, thus pumping blood it receives throughout the body. The rhythmic contractions of the heart are initiated and controlled by electrical impulses (also referred to herein interchangeably as electrical signals or electrical charges) produced by special cells in the heart known as pacemaker cells. These cells form a network throughout various regions of the heart, creating what is referred to as the electrical conduction system of the heart. As an electrical impulse conducts through the electrical conduction system of the heart through various regions of the heart, these regions in turn contract thus pumping blood out of the heart. Reference is now made to FIG. 1A which is a schematic illustration of the major parts of a human heart, from a coronal cross-sectional view, generally referenced 10, and the electrical conduction system of heart 10, as is known in the prior art. Heart 10 is made up of four chambers, separated into a left side and a right side. Each of the left side and the right side of heart 10 respectively include two chambers. These chambers are a right atrium 12, a left atrium 14, a right ventricle 16 and a left ventricle 18. Right atrium 12 and right ventricle 16 are substantially coupled with one another however they are separated into two chambers by a set of valves 20, known collectively as the tricuspid valve (also referenced as tricuspid valve 20). Left atrium 14 and left ventricle 18 are also substantially coupled with one another however they are also separated into two chambers by a set of valves 22, known collectively as the mitral valve (also referenced as mitral valve 22). Both tricuspid valve 20 and mitral valve 22 are unidirectional valves, only allowing blood to flow from an atrium to a ventricle and thus preventing blood from flowing from a ventricle into an atrium. In normal, healthy human hearts, right atrium 12 and right ventricle 16 are completely sealed from left atrium 14 and left ventricle 18 by a wall 26, known as the septum (also referenced as septum 26).
Each side of the heart is responsible for pumping blood through a major loop or cycle in a body (not shown). The right side of the heart receives deoxygenated blood (not shown) from the body and pumps the deoxygenated blood to the lungs (not shown) where the blood is re-oxygenated. The left side of the heart receives the re-oxygenated blood (not shown) from the lungs and pumps the re-oxygenated blood to the body. Right atrium 12 receives deoxygenated blood from the body via the superior vena cava (not shown) and the inferior vena cava (not shown), which both empty the deoxygenated blood collected from all the cells and tissues of the body into right atrium 12. As right atrium 12 fills with blood, the deoxygenated blood is pushed through tricuspid valve 20 into right ventricle 16. Once right ventricle 16 is filled, it in turn pumps the deoxygenated blood into the pulmonary artery (not shown), which transports the deoxygenated blood to the lungs for re-oxygenation. Re-oxygenated blood is brought from the lungs to left atrium 14 via the pulmonary vein (not shown). As left atrium 14 fills with blood, the re-oxygenated blood is pushed through mitral valve 22 into left ventricle 18. Once left ventricle 18 is filled, it in turn pumps the re-oxygenated blood into the aorta (not shown), which transports the re-oxygenated blood to the cells and tissues of the body via a network of arteries. Right ventricle 16 and left atrium 14 thus form the pulmonary loop or cycle in the body as blood is transferred to and from heart 10 to the lungs. Right atrium 12 and left ventricle 18 thus form the circulatory loop or cycle in the body as blood is transferred to and from heart 10 to the cells and tissues of the body.
Heart 10 is substantially composed of two types of cells, known as myocardiocytes and pacemaker cells. Myocardiocytes are a type of involuntary muscle cell that can contract upon the reception of electrical impulses. Right atrium 12, left atrium 14, right ventricle 16 and right ventricle 18 (i.e., a majority of heart 10) are composed of a plurality of myocardiocytes 24, which all contract upon receiving electrical impulses. The contraction of myocardiocytes is what results in the pumping action of heart 10, thus enabling the atria (plural of atrium) of heart 10 to pump blood in the ventricles and enabling the ventricles to pump blood to the lungs and the rest of the body. As mentioned above, the pacemaker cells (not specifically referenced) are responsible to generating electrical impulses which travel through the various chambers of the heart, thus causing the pumping action of the heart.
The electrical conduction system of heart 10 includes a sinoatrial (herein abbreviated SA) node 28, an atrioventricular (herein abbreviated AV) node 30, an AV bundle 32 (also known as and referenced as bundle of HIS 32), a right bundle branch 34, a left bundle branch 36 and a plurality of fibers 38 (also known as and referenced as plurality of Purkinje fibers 38). Each one of SA node 28, AV node 30, bundle of HIS 32, right bundle branch 34, left bundle branch 36 and plurality of Purkinje fibers 38 is composed of pacemaker cells. Pacemaker cells are unique in that they can involuntarily and rhythmically produce electrical impulses and can also transfer electrical impulses they receive. In normal hearts, the pacemaker cells (not shown) in SA node 28 produce about 100 electrical impulses per minute, the pacemaker cells (not shown) in AV node 30 produce about 40-60 electrical impulses per minute and the pacemaker cells (not shown) in bundle of HIS 32, right bundle branch 34, left bundle branch 36 and plurality of Purkinje fibers 38 produce about 30-40 electrical impulses per minute. Since the pacemaker cells in SA node 28 produce electrical impulses quicker than any other area of heart 10, SA node 28 functions as the primary or normal pacemaker of heart 10. SA node 28 is located in right atrium 12 and is coupled with AV node 30 via the internodal tracts (not shown). AV node 30 is located in septum 26, right at the intersection of all the chambers of heart 10. Bundle of HIS 32 branches off from AV node 30 along septum 26 and splits into right bundle branch 34 and left bundle branch 36. Right bundle branch 34 lines the interior wall of right ventricle 16 whereas left bundle branch 36 lines the interior wall of left ventricle 18. The distal end (not labeled) of each of right bundle branch 34 and left bundle branch 36 branches off into a network of smaller pacemaker cells which form plurality of Purkinje fibers 38. Plurality of Purkinje fibers 38 also lines the interior walls of right ventricle 16 and left ventricle 18, in the direction towards right atrium 12 and left atrium 14 respectively.
Reference is now made to FIG. 1B which is a schematic illustration of the heart shown in FIG. 1A, from a coronal cross-sectional view, showing the flow of electrical impulses through the electrical conduction system of the heart, generally referenced 50, as is known in the prior art. Identical parts of heart 50 in FIG. 1B and heart 10 in FIG. 1A are labeled using equivalent reference numbers. In normal hearts (i.e., where the physiology of the heart is normal), SA node 28 initiates an electrical impulse (not labeled). The electrical impulse travels through right atrium 12 and left atrium 14, shown by a plurality of arrows 52. This traveling electrical impulse causes both right atrium 12 and left atrium 14 to contract simultaneously, thus causing blood to flow from right atrium 12 into right ventricle 16 and from left atrium 14 into left ventricle 18. The electrical impulse eventually reaches AV node 30 which causes a delay in the transfer of the electrical impulse to bundle of HIS 32. This delay is known as the AV delay (explained in more detail below in FIG. 2A) and substantially enables both atria to empty completely of blood. After the AV delay, AV node 30 transfers the electrical impulse to bundle of HIS 32, shown by an arrow 54. Bundle of HIS 32 in turn transfers the electrical impulse to right bundle branch 34, shown as a plurality of arrows 56 and left bundle branch 36, shown as a plurality of arrows 58, thus causing right ventricle 16 and left ventricle 18 respectively to begin contracting. The split electrical impulse is then transferred to plurality of Purkinje fibers 38, shown by a plurality of arrows 60, thus causing the rest of right ventricle 16 and left ventricle 18 respectively to finish contracting. In normal hearts, the electrical impulse travels simultaneously down right bundle branch 34 and left bundle branch 36 and their respective networks of Purkinje cells, thus causing both ventricles to pump and contract simultaneously. Thus, in normal healthy human hearts, the electrical impulse initiated in SA node 28 causes right atrium 12 and left atrium 14 to substantially simultaneously pump blood into right ventricle 16 and left ventricle 18 respectively and then to substantially simultaneously cause right ventricle 16 and left ventricle 18 to pump blood respectively to the lungs and body.
The electrical impulse received by AV node 30 from SA node 28 substantially overrides any natural electrical impulses AV node 30 would generate on its own. Thus once AV node 30 receives an electrical impulse from SA node 28, and after the AV delay, the pacemaker cells in AV node 30 effectively transfer the electrical impulse from SA node 28 by generating their own electrical impulse. The same is true for electrical conduction in bundle of HIS 32, right bundle branch 34, left bundle branch 36 and plurality of Purkinje fibers 38. Each time heart 50 beats, SA node 28 is substantially sending out an electrical impulse which travels through heart 50, thus causing its various chambers to contract and pump blood through the two major loops in the body as described above.
Medical conditions of the heart in general can be broken down into two major categories, those that relate to issues with the blood flow system of the heart and those that relate to issues with the electrical conduction system of the heart. Medical conditions relating to issues with the electrical conduction system of the heart are generally referred to as cardiac arrhythmias and include conditions such as tachycardia (when SA node 28 produces electrical impulses too rapidly), bradycardia (when SA node 28 produces electrical impulses too slowly), conditions where SA node 28 produces electrical impulses that have an irregular rhythm and conditions known as bundle branch block where one or both of the bundle branches in heart 50 do not conduct electrical impulses. Bundle branch block can prevent the ventricles from pumping blood altogether, leading to cardiac arrest, or can cause one ventricle to pump blood out of sync with the other ventricle, thus leading to inefficient blood circulation in the body and thus causing other health issues.
Cardiac arrhythmias are assessed by monitoring the electrical activity of the heart. This is most commonly done via electrocardiography, where a set of ten electrodes are attached to the surface of the body, primarily around the chest area where the heart is located. These electrodes are commonly referred to as surface electrodes since they monitor the electrical activity of the heart from the surface of the skin. The recordings of these electrodes produce twelve different readings of the electrical activity (usually either a measure of the current or voltage of the electrical impulses) of the heart over time, which is known as an electrocardiogram (herein abbreviated ECG). These twelve different readings are referred to as leads and are the result of different combinations of electrical signals received from each of the ten electrodes. These twelve different leads are known by the following abbreviations: V1, V2, V3, V4, V5, V6, I, II, III, aVR, aVL and aVF and can give a person skilled in the art, such as a cardiologist, a plethora of information regarding the electrical conduction system of the heart of a patient. Since the SA node of the heart sends out electrical impulses rhythmically, an ECG should produce a recurring pattern of electrical activity over time showing how electrical impulses travel through the heart. Reference is now made to FIG. 2A which is a schematic illustration of an ECG, generally referenced 70, showing the classification of various waveforms in a single electrical impulse traveling through a human heart (not shown), as is known in the prior art. ECG 70 is printed on a specialized boxed grid 71, where the horizontal (i.e., left-right) axis (not shown or labeled) represents time and the vertical (i.e., up-down) axis (not shown or labeled) represents the amplitude of electrical activity. Each box measures 1 millimeter (herein abbreviated mm) and every group of five boxes, representing 5 mm, is demarcated with a thicker line (not labeled), such that ECG 70 can be read at a resolution of 1 mm or 5 mm. Electrical activity can be represented as a voltage or a current. In FIG. 2A, electrical activity is represented as a voltage. Specialized boxed grid 71 is used to enable workers skilled in the art to easily interpret ECG 70 by merely looking at how many boxes a given part of a registered signal 81 covers in the horizontal and vertical directions. Sections 79, 92 and 94 in FIG. 2A show a legend indicating how much time each box and each group of five boxes represents in the horizontal direction and how much voltage each box and each group of five boxes represents in the vertical direction. For example, as shown in section 79, each box in the vertical direction represents a voltage of 0.1 millivolts (herein abbreviated mV) and each group of five boxes represents 0.5 mV. In section 92, each box in the horizontal direction represents 0.04 seconds, which is equivalent to 40 milliseconds (herein abbreviated ms). In section 94, each group of five boxes in the horizontal direction represents 0.2 seconds, which is equivalent to 200 ms.
Registered signal 81 represents a schematic illustration of a theoretical electrical impulse signal of a human heart over the course of one heartbeat registered by the ten electrodes of an ECG. Since the voltage amplitude is measured in the vertical direction, any sections of horizontal lines in registered signal 81 represent no electrical activity (such as a PR segment 80, as described below) in the heart whereas sections or segments that change over time in the vertical direction (such as a QRS interval 74, as described below) represent changes in electrical activity in the heart. A dotted line 87, added for emphasis, shows an arbitrary 0 volts line. As voltages can be positive or negative, electrical activity in the vertical direction can be registered above and below the 0 volts line thus representing differences in the polarity of the voltage of the electrical impulse as it travels through the heart.
Registered signal 81 represents the electrical signal of a single heartbeat and starts at a point 83 and ends at a point 85. As mentioned above, an electrical impulse is generated by the SA node and propagates through the atria of the heart. This is seen in ECG 70 as a wave 72, known in the art as a P-wave. P-wave 72 thus represents the traveling electrical impulse propagating through the atria and thus pushing blood from the atria into their respective ventricles. P-wave 72 is followed by P-R segment 80, which is a period of no electrical activity in the heart. P-R segment 80 represents the AV delay experienced in the heart where the AV node delays the propagation of the electrical signal to the bundle of HIS, thus allowing the atria to empty of blood. P-R segment 80 is followed by three waves, a wave 73, known as the Q-wave, a wave 75, known as the R-wave and a wave 77, known as the S-wave. In general, Q-wave 73, R-wave 75 and S-wave 77 are grouped together to form ORS interval 74, which is also known as the QRS complex. QRS complex 74 represents the propagation of the electrical impulse from the AV node to the bundle of HIS, down through the right and left bundle branches and into the plurality of Purkinje fibers. Thus ORS complex 74 represents the contraction of the right and left ventricles as they pump blood respectively to the lungs and body. QRS complex 74 is followed by an S-T segment 84, again during which no electrical activity is registered in the heart. Following S-T segment 84 is a wave 76, known as the T-wave, followed by a wave 90, known as the U-wave. Either side of U-wave 90 in the horizontal direction (i.e., over time) may be preceded and followed by a short period of no electrical activity. Electrical impulses are propagated through the heart by an electrochemical reaction involving calcium and potassium. Electrical charge can flow via the depolarization of a resting state of the cells of the heart. Once depolarized, the cells of the heart must repolarize in order to allow electrical charge to flow again. T-wave 76 represents the repolarization of the cells of the heart in the ventricles, whereas U-wave 90 represents the repolarization of the cells of the heart in the plurality of Purkinje fibers. U-wave 90 is not always visible in an actual ECG. Repolarization of the cells of the heart in the atria usually occurs during P-R segment 80 and is not usually registered or visible on an ECG. Repolarization electrochemically is substantially equivalent to the physical relaxation of the cells of the heart. Thus T-wave 76 and U-wave 90 respectively represent the relaxation of the ventricles and the plurality of Purkinje fibers.
After U-wave 90, another electrical impulse initiated by the SA node is expected, thus another P-wave (not shown) is expected. As shown in FIG. 2A, the time interval between a P-wave and a subsequent P-wave is known as a P-P interval 78 and substantially represents the heart rate of the heart, or the rate at which the heart is beating. Other known time intervals which are commonly used by skilled workers in the art include a P-R interval 82, measured from the start of P-wave 72 to the start of QRS complex 74, a Q-T interval 88, measured from the start of ORS complex 74 to the end of T-wave 76 and an S-T interval 86, measured from the start of S-T segment 84 to the end of T-wave 76. P-R interval 82 is substantially a measure of how much time it takes an electrical impulse to travel from the SA node, through the AV node into the bundle of HIS. Q-T interval 88 is substantially a measure of how much time it takes the ventricles to depolarize, pump blood out to the lungs and body and then repolarize before the next electrical impulse arrives.
As shown, a typical P-P interval may last about 750 ms (about three quarters of a second). Average human resting heart rates (i.e., when a person with a normal heart is not engaged in physical or strenuous activity) can vary between 60 to 100 beats per minute, translating into a range of between 600-1200 ms for an average P-P interval. A typical P-wave may last about 80 ms, a typical P-R segment may last between 50-120 ms, a typical QRS complex may last about 80-120 ms, a typical S-T segment may also last between 80-120 ms and a typical T-wave may last about 160 ms.
P-R segment 80 demarcated by a dotted ellipse 96, which is shown in an expanded view below ECG 70 in FIG. 2A. P-R segment 80 represents the AV delay in the propagation of electrical impulses received from the SA node to the bundle of HIS and is itself subdivided into three separate portions. The AV delay includes an intra-atrial conduction time 98, an AV nodal conduction time 100 and an infra-Hisian conduction time 102. Intra-atrial conduction time 98 represents the amount of time required for the electrical impulse to leave the SA node and arrive at the AV node and can last between 5-10 ms. AV nodal conduction time 100 represents the built-in delay in the AV node which slows the propagation of the received electrical impulse to the bundle of HIS, thus allowing the atria to empty of blood and the ventricles to fill with that blood. AV nodal conduction time 100 represents the bulk of P-R segment 80 and can last between 70-300 ms. Infra-Hisian conduction time 102 represents the amount of time required for the electrical impulse to leave the AV node and travel down the bundle of HIS to the right and left bundle branches and can last between 40-55 ms.
Reference is now made to FIG. 2B which shows an actual ECG of the heart of a healthy individual, generally referenced 110, as is known in the prior art. ECG 110 is shown on the specialized boxed paper described above in FIG. 2A. Clearly visible in ECG 110 are individual lines 113 in the vertical and horizontal directions demarcating individual boxes (each measuring 1 mm) as well as emphasized lines 111 in the vertical and horizontal directions demarcating groups of five boxes (in total, each group measuring 5 mm). As seen in ECG 110, the twelve different leads of the ten electrodes are laid out on three separate lines of registered electrical signals. For example, registered electrical signal 115A shows the leads of I, aVR, V1 and V4, registered electrical signal 115B shows the leads of II, aVL, V2 and V5 and registered electrical signal 115C shows the leads of III, aVF, V3 and V6. The twelve different leads, referenced as registered electrical signals 115A-115C are really twelve different readings of the same electrical impulse generated by the SA node and propagated through the heart. As can be seen from lead the heart of a healthy individual exhibits a P-wave 112, a QRS complex 114 and a T-wave 116. U-waves are visible in lead I. A P-P interval 118A is shown for lead I. In lead II, two consecutive P-P intervals 118B and 118C are shown next to one another. What stands out clearly in ECG 110 is the similar, rhythmic pattern of each P-P interval for each lead. Whereas P-P interval 118A has a different waveform (i.e., shape) from P-P intervals 118B and 118C, due to the registration of the electrical impulse of the heart by different electrodes, the waveforms of P-P intervals 118B and 118C are substantially similar. This is what a healthy human heart is supposed to look like in an ECG.
Reference is now made to FIG. 3A which is a schematic illustration of a human heart suffering from left bundle branch block, from a coronal cross-sectional view, generally referenced 130, as is known in the prior art. Heart 130 is substantially similar to heart 10 (FIG. 1A) and heart 50 (FIG. 1B), however not all major parts of heart 130 are labeled to avoid excessive reference numbers in FIG. 3A. FIG. 3A shows how the electrical conduction system of heart 130 is altered when a patient suffers from left bundle branch block (herein abbreviated BBB). Heart 130 includes an SA node 132, an AV node 136, a bundle of HIS 138, a right bundle branch 144, a left bundle branch 148, a plurality of right side Purkinje fibers 156 and a plurality of left side Purkinje fibers 158. The conduction pathway of electrical impulses from SA node 132 to AV node 136 is shown via a plurality of arrows 134. The conduction of electrical pulses from AV node 136 to bundle of HIS 138 is shown as an arrow 140.
A patient suffering from left BBB substantially has a condition in which electrical impulses originating from the SA node which propagate to the bundle of HIS do not continue down and propagate through the left bundle branch and through the left side Purkinje fibers of the heart. As shown, electrical impulses travel down right bundle branch 144, as shown by a plurality of arrows 142 and eventually into plurality of right side Purkinje fibers 156, shown by an arrow 154, However, electrical impulses do not travel left bundle branch 148 and into plurality of left side Purkinje fibers 158, as shown by crossed-through arrows 146, 150 and 152. Left BBB may present itself in patients differently. For example, an assessment of a patient with left BBB may not be able to pinpoint where along left bundle branch 148 the electrical impulses of the SA node cease to propagate. An individual may have no electrical conduction along left bundle branch 148 starting from a point 160A, just below bundle of HIS 138, starting from a point 160B or a point 160C, along various points of left bundle branch 148, or starting from a point 160D, wherein left bundle branch 148 conducts the electrical impulse however plurality of left side Purkinje fibers 158 do not. In each of these scenarios, a patient would be diagnosed with left BBB, even though in some of the scenarios, the left ventricle (not labeled) would partially pump blood to the body (not shown). Left BBB can also present itself in an individual in which electrical impulses are conducted through the left bundle branch and into the plurality of left side Purkinje fibers, however at a rate significantly slower than the rate at which electrical impulses propagate through the right bundle branch and the plurality of right side Purkinje fibers. As mentioned above, pacemaker cells in the heart can rhythmically generate electrical pulses and also propagate electrical pulses received. Therefore the left ventricle in the heart of an individual with left BBB having no electrical conduction starting from point 160A may still contract due to electrical impulses eventually propagating from right bundle branch 144 and plurality of right side Purkinje fibers 156 into the left ventricle. The left ventricle in the heart of such an individual may also contract if the pacemaker cells in left bundle branch 148, plurality of left side Purkinje fibers 158 or both produce native electrical impulses on their own. However as mentioned above, the pacemaker cells located in those parts of the heart produce electrical impulses at a rate which might be twice as slow as the rate at which SA node 132 produces electrical impulses.
In general, individuals having a condition of left BBB have a heart in which the left ventricle does not contract and pump blood to the body in sync with the right ventricle (not labeled). In addition, the left ventricle may not pump as efficiently as the right ventricle, since it may be receiving electrical impulses with a significant delay and at a significantly slower rate. Less efficient pumping translates into a lowered ejection fraction (i.e., the percent of blood pumped from a ventricle into an artery) of blood from the ventricle, which can lead to other health issues including congestive heart failure which is a condition resulting from poor cardiac output. A similar condition known as right BBB exists, in which electrical conduction may be blocked or delayed along right bundle branch 144, plurality of right side Purkinje fibers 156 or both. Left BBB is considered a more serious condition than right BBB since the right ventricle only needs to pump blood to the lungs, which are adjacent to the heart, whereas the left ventricle needs to pump blood to the entire body.
Reference is now made to FIG. 3B which shows an actual ECG of the heart of an individual having left BBB, generally referenced 170, as is known in the prior art. As seen in lead III, two consecutive P-waves 172A and 172B are visible thus forming a P-P interval 174. In comparison to lead III from ECG 110 (FIG. 2B) however, P-P interval 174 has a very different waveform than that of a healthy heart. As seen in lead aVL, P-waves 176A and 176B are not well defined, which are each respectively followed by P-R segments 178A and 178B. In addition, QRS-complexes 180A and 180B are very wide, especially the R-waves (not labeled), indicating the lag in time in electrical conduction to the left ventricle as a result of the left bundle branch block. Typically in patients with left BBB, conduction to the left ventricle is via cell-to-cell conduction starting in the right ventricle. This type of electrical conduction is much slower than electrical conduction via the specialized conduction system of the heart (as shown above in FIG. 1B, including the bundle of HIS, the right and left bundle branches and the plurality of Purkinje fibers). In left BBB, the specialized conduction system of the left side of the heart does not function properly. Electrical conduction to the left side of the heart nonetheless occurs due to slower cell-to-cell conduction which originates in the right ventricle. Myocardial cell-to-cell conduction is much slower than the specialized electrical conduction in the heart, thus explaining the wide QRS complex seen in left BBB patients.
Patients with right or left BBB can be treated by using cardiac resynchronization therapy (herein abbreviated CRT) in which a device, known as a pacemaker or artificial pacemaker, is inserted into the patient, that takes over the role of providing electrical impulses to the right bundle branch and left bundle branch. This action is referred to as pacing, since the artificial pacemaker takes over the role of a portion of the pacemaker cells in the heart. Pacemakers usually include two parts, a can and a plurality of leads. Reference is now made to FIG. 4, which is a schematic illustration of a pacemaker coupled with a heart, from a coronal cross-sectional view, generally referenced 190, for artificially pacing the heart, as is known in the prior art. As shown, a pacemaker 192 has been inserted into a patient (not shown) and is coupled with a heart 193, for artificially pacing it. Pacemaker 192 includes a can 194 and a plurality of leads 196A, 196B and 196C. Plurality of leads 196A-196C is coupled with can 194. Can 194 is usually positioned subcutaneously in the chest area of the patient. Can 194 includes a processor (not shown), a battery (not shown) and optionally at least one capacitor (not shown). The battery is used for powering the processor and providing electrical impulses (i.e., synchronization impulses) to plurality of leads 196A-196C. Some pacemakers may include an implantable cardioverter defibrillator (herein abbreviated ICD). In such pacemakers, the ICD functionality may require a high voltage electrical impulse and hence at least one capacitor can be used to serve that purpose. In these pacemakers, the battery can be used for building up a high voltage charge on the at least one capacitor. As some pacemakers may not have such an ICD function available, the at least one capacitor is not included and is thus an optional element in can 194. The processor receives measurements of the electrical activity of the heart via at least one of plurality of leads 196A-196C and decides when electrical pulses should be delivered to heart 193, how often and at what voltage.
As shown, heart 193 includes a right atrium 200, a right ventricle 204, a left atrium 210 and a left ventricle 208. Known pacemakers usually include at least three leads which are usually coupled intravascularly to the heart via the superior vena cava (not shown). A first lead, lead 196A, is positioned in right atrium 200, where the SA node (not shown) is located. A distal end 198 of lead 196A is used to sense electrical activity in right atrium 200, such as when a P-wave (not shown) was initiated by the SA node, thus indicating that right atrium 200 and left atrium 210 are contracting. Distal end 198 can also be used to send electrical impulses to right atrium 200 and left atrium 210, thus replacing the role of the SA node. A second lead, lead 196B, is positioned in right ventricle 204, usually via the tricuspid valve (not labeled), such that its distal end 202 is positioned near the plurality of Purkinje fibers (not labeled) located at the distal end of the right bundle branch. A third lead, lead 196C, is positioned in left ventricle 208. A distal end 206 of lead 196C is usually inserted into the heart via the superior vena cava into right atrium 200, and is then routed to the coronary sinus (not shown). Distal end 206 is thus shown as a dotted line. Lead 196B is used to pace right ventricle 204 and lead 196C is used to pace left ventricle 208 via the coronary sinus.
Pacemaker 192 works as follows. Lead 196A includes a sensor (not shown) for sensing atrial contractions (i.e., a P-wave) in right atrium 200 and left atrium 210. When a P-wave is detected, the sensor in lead 196A sends a signal back to the processor in can 194 indicative of the P-wave. Upon receiving the indication of the P-wave, the processor is programmed to wait a predetermined amount of time which is supposed to approximate the normal physiological AV delay of the AV node (not labeled) and then sends an electrical impulse down leads 196B and 196C to pace right ventricle 204 and left ventricle 208. The electrical impulse sent down leads 196B and 196C may be sent simultaneously or nearly simultaneously thus causing both right ventricle 204 and left ventricle 208 to contract at substantially the same time. The left BBB in the natural electrical conduction to the left bundle branch is thus bypassed by the electrical impulse sent down lead 196C, and the simultaneous or near simultaneous contraction of both right ventricle 204 and left ventricle 208 thus attempts to negate any physiological consequences of the left BBB.
Pacemaker systems and CRT methods (also referred to as pacing methods) based on the principles outlined in FIG. 4 are known in the art. In addition, cardiac resynchronization therapy methods are known in the art. For example, US Patent Application No. 2010/0087888 A1 to Maskara, entitled “Methods and apparatuses for cardiac resynchronization therapy mode selection based on intrinsic conduction” is directed to systems and methods for selecting a cardiac resynchronization therapy (CRT) mode, the selection being between a synchrony optimization mode and a preload optimization mode. The system and method involve sensing electrocardiogram (ECG) data for a patient, identifying a parameter from the sensed ECG, such as a PR interval, comparing the parameter to a threshold and selecting a CRT mode. The selected CRT mode is based on the comparison of the parameter to the threshold. The synchrony optimization mode may be selected if the parameter is less than the threshold, and may optimize CRT for fusion between a left ventricular pulse and an intrinsic wavefront. The preload optimization mode may be selected if the parameter is greater than the threshold, and may optimize CRT for fusion between respective wavefronts of the left ventricular pace and a right ventricular pace.
US Patent Application No. 2013/0035738 A1 to Karst et al. and assigned to Pacesetter, Inc., entitled “Methods and systems for determining pacing parameters based on repolarization index” is directed to methods and systems for determining pacing parameters for an implantable medical device (IMD). The methods and systems are intracardiac and provide electrodes in the right atrium (RA), right ventricle (RV) and left ventricle (LV). RV cardiac signals and LV cardiac signals are sensed at an RV electrode and an LV electrode, respectively, over multiple cardiac cycles, to collect global activation information. A T-wave in the LV cardiac signal is identified. A repolarization index is calculated based at least in part on a timing of the T-wave identified in the LV cardiac signal. At least one pacing parameter is then set based on the repolarization index. The set pacing parameter represents at least one of an AV delay, an inter-ventricular interval and an intra-ventricular interval. Optionally, the methods and systems may deliver an RV pacing stimulus at the RV electrode such that the LV cardiac signal sensed thereafter includes the RV pacing stimulus followed by a T-wave. The methods and systems determine a waveform metric such as at least one of a QT interval, T-wave duration and T-wave amplitude, and utilize the waveform metric to determine the repolarization index.
U.S. Pat. No. 8,160,700 issued to Ryu et al. and assigned to Pacesetter, Inc., entitled “Adaptive single site and multi-site ventricular pacing” is directed to methods for optimizing cardiac therapy using single site or multi-site pacing. One method includes the procedures of delivering a cardiac pacing therapy using an electrode configuration for left ventricular, single site pacing or left ventricular, multi-site pacing, measuring a series of interventricular conduction delays using the left ventricular pacing and right ventricular sensing (IVCD-LR), comparing the interventricular conduction delay values to a limit and, based on the comparison, deciding whether to change the electrode configuration for the left ventricular pacing. Another method includes the procedures of measuring a plurality of interventricular conduction delays using right ventricular pacing and left ventricular sensing wherein each interventricular conduction delay (IVCD-RL) corresponds to a different electrode configuration for a right ventricular lead, measuring a plurality of interventricular conduction delays using left ventricular pacing and right ventricular sensing wherein each interventricular conduction delay (IVCD-LR) corresponds to a different electrode configuration for the right ventricular lead, determining the shortest conduction delay, and based on the shortest conduction delay, selecting an electrode configuration for the right ventricular lead for use in right ventricular pacing.
U.S. Pat. No. 6,556,859 issued to Wohlgemuth et al. and assigned to Medtronic, Inc., entitled “System and method for classifying sensed atrial events in a cardiac pacing system” is directed to a system for classifying distinct signals sensed from an electrode of an implantable cardiac pacing system positioned within an atrium of a heart of a patient. The cardiac pacing system includes a pulse generator for generating pacing pulses and a controller for controlling the operation of a pacemaker. The method includes collecting atrial event signals consisting of P-wave signals and far field R-wave signals. An interim form factor histogram is generated based upon a form of collected atrial event signals. The interim form factor histogram includes an interim P-wave form factor histogram and an interim far field R-wave form factor histogram, each having bins of atrial event signals. A previously generated form factor histogram is weighted and combined with the interim form factor histogram to create a representative form factor histogram. The representative form factor histogram is analyzed to determine if a minimal safety margin is located between the representative P-wave form factor histogram and the representative far field R-wave form factor histogram. Atrial event signals are classified by form as either P-wave signals or far field R-wave signals based upon the representative form factor histogram.